Last Updated: December 6, 2020

How to add Cyanuric Acid to Your Pool

Written By: Pool Care Guide

What Are the Ideal Levels of Cyanuric Acid (CYA)?

It is likely that you are here to find the ideal levels of cyanuric acid and how much to add to achieve them. If that’s all you need, the two tables below should help. If you want to know about science and potential complications, you can keep reading after that.

Ideal Total Cyanuric Acid Levels

Direct Sunlight: Freshwater PoolDirect Sunlight: Saltwater PoolIndoor PoolIf Using an ORP Controller
40 to 80 PPM80 PPM0 PPM - You don’t need CYA if there isn’t any direct sunlight30 to 50 PPM

Ounces of Cyanuric Acid Needed To Increase Cyanuric Acid PPM

To calculate the correct dosage, you will need to know how many gallons of water your pool is holding. These amounts can differ from product to product, so check the instructions on the label. Generally speaking, here is how much cyanuric acid you will need to add to increase the cyanuric acid by the associated PPM amounts:

Pool Size10,000 Gallons20,000 Gallons30,000 Gallons
+10 PPM13 Ounces1 Pound, 10 Ounces2 Pounds 7 Ounces
+20 PPM1 Pound, 10 Ounces3 Pounds, 4 Ounces4 Pounds, 14 Ounces
+30 PPM2 Pounds, 7 Ounces4 Pounds, 14 Ounces7 Pounds, 5 Ounces
+40 PPM3 Pounds, 4 Ounces6 Pounds, 8 Ounces9 Pounds, 12 Ounces
+50 PPM4 Pounds, 1 Ounce8 Pounds, 2 Ounces12 Pounds, 3 Ounces
+60 PPM4 Pounds, 14 Ounces9 Pounds, 12 Ounces14 Pounds, 10 Ounces
+70 PPM5 Pounds, 11 Ounces11 Pounds, 6 Ounces17 Pounds, 1 Ounce
+80 PPM6 Pounds, 8 Ounces13 Pounds19 Pounds, 8 Ounces

Sometimes the ideal levels of cyanuric acid conflict with local governmental regulations. If you are maintaining a public pool, you will want to check up on the local ordinances. The maximum levels might be as low as 30 PPM or as high as 100 ppm.

How to Add Cyanuric Acid to Your Pool

First, if you are adding chlorine into your pool, you might already be adding cyanuric acid. If you are buying stabilized chlorine, it’s going to be in the form dichlor or trichlor (Chlorine + Cyanuric Acid). Chlorine is removed from a pool over time, but cyanuric acid only leaves the pool if it is splashed or drained out of it.

If you are adding a chlorine puck that contains cyanuric acid, you will have different dispersal options that are discussed here. If you are adding pure cyanuric acid:

  • Step 1: Fill a large bucket with warm water
  • Step 2: Add the Cyanuric Acid to the bucket of water
  • Step 3: Wait for it to dissolve.
  • Step 4: Pour it to the skimmer.
  • Step 5: Run the pool pump for a few hours.

Not all packaging instructions say this, but it is recommended for the health of your pool’s filters. You are adding acid which can damage pool filters over time. Dissolving it in the bucket limits the damage. 

What is Cyanuric Acid?

Cyanuric Acid is a money saver. As far as pools go, the only function that cyanuric acid serves is to stabilize chlorine. If Chlorine is left to itself, the UV light will quickly remove it from the water through evaporation and a process called photolysis (Photo = Light, Lysis = Separation). On a hot day with direct sunlight, UV light has the potential to remove half of the free chlorine in only 17 minutes. The cyanuric acid provides a weak bond that gives the chlorine something on which to latch. That attachment protects the chlorine from electrolysis so the chlorine doesn’t evaporate soon after it has been added to the pool.

Chemically speaking, what makes cyanuric acid, an acid, is that it donates protons by releasing positively charged hydrogens into the water. This has the potential to gradually throw off the pH balance of your pool, so adding cyanuric acid can cause problems such as deteriorating pool equipment. Additional intervention might be required to neutralize those added charged hydrogen atoms.

Delving just a bit further, Cyanuric acid belongs to the family of triazine compounds. These are ring-shaped molecules that contain three carbon atoms and three nitrogen atoms. Of course, they also have positively charged hydrogen atoms mixed into them since they are acids.

Don’t Use too much Cyanuric Acid

Free Chlorine Versus Chloramines (Stabilized Chlorine)

Remember how we said that chlorine needs to be stabilized? This is true, but we don’t want it to be too stable. If there is too much CYA in the pool, the chlorine will keep bumping into the CYA instead of the bacteria that it needs to destroy. It won’t be as molecularly available. 

Chlorine is extremely destructive to bacteria and can kill most bacteria within seconds of contact. It’s so destructive that our white blood cells inject the very same chlorine bleach directly into bacteria.

We need the reactive chlorine compounds of hypochlorous acid (HOCl) and the hypochlorite (OCl-) ion that form from the mixing of chlorine (Cl) and water (H2O). Unfortunately, these two compounds are easily broken apart by UV light. 

Given enough time, there are three ways that chlorine is used up. Some of the chlorine binds to bacteria and destroys them. Some of it quickly evaporates. The rest of the chlorine will combine with CYA and remain stabilized and protected from the UV light as one of the three weakly-bonded forms of Chloramines (CYA + Chlorine): monochloramine, dichloramine, and trichloramine. These weak bonds protect the Chlorine from the oxidizing power of the sun’s UV light, but the bond is also weak enough that the chlorine can occasionally break away to destroy bacteria.

Additional Sources of CYA

If you were surprised by how much CYA is or was in your pool, you may want to take a look at the ingredients of your chlorine product. As we mentioned earlier, many of them contain chlorine and CYA. That means that you are adding CYA every time that you add chlorine. If you look at the labels of these chlorine/CYA products, you will see at least one of these three ingredients:

  • potassium dichloroisocyanurate
  • sodium dichloroisocyanurate
  • trichloroisocyanurate

Cyanuric Acid can also be harbored in plaster walls, calcium scale build-up, and pool filters. If you refill your pool and the levels of CYA levels seem too high, that is probably going to be the reason for it. A good cleaning might be in order, and you might want to clean or backwash your pool filter(s). If the CYA levels were really high, maybe you should wait a day before adding any more Cyanuric Acid to the pool. It might help you to get a better idea of what CYA is already there so that you don’t add too much to the water. 

How to Remove or Reduce Cyanuric Acid

If your CYA is too high, your chlorine will not be able to kill the bacteria faster than the bacteria will grow. Cyanuric acid levels do not change much over time since cyanuric acid doesn’t evaporate like chlorine. To reduce the CYA-to-water ratio, you will need to either dilute it by adding water to your pool or by draining and refilling it.

How Often Do You Need to Add Cyanuric Acid?

You will find a variety of answers across the internet. Generally speaking, you probably won’t need to add cyanuric acid more than once or twice a year. When it is in the pool, the levels will only change if it is splashed out or diluted. Even though you aren’t likely to need to add more, you should still check your pool’s chemistry each week.

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